Within most integrated circuits (“ICs”) there is usually one data path that requires more time to propagate valid data than all other data paths. The data path that requires the longest propagation time before it may be sampled or is resolved is known as the critical path of the IC. A circuit path may be slow due, for example, to a greater number of device delays within the critical path or a greater signal travel distance.
The maximum speed at which the IC may operate is limited by the critical path of the IC. The reason for this is that the critical path presents the longest delay path and the clock rate cannot be increased beyond the point at which the clock cycle time is equal to the propagation delay of signals traveling along the critical path.
Since the maximum clock speed of an IC is limited by its critical path, locating the critical path (LCP) is an important design task. Once the critical path has been identified, the design may be optimized to reduce the time it takes a signal to propagate along the critical path. LCP and design optimizations may be repetitive tasks. Each time the design is optimized to reduce the delay length of a critical path, a new critical path may arise. Large scale IC design is complicated by the millions of possible critical paths. LCP becomes the task of locating the proverbial needle in a haystack. As such, sophisticated design and testing tools are required.